Thermosetting polyurethanes with stable and large second-order optical nonlinearity

A two-component, thermally-curable second-order nonlinear optical material, based on the polyurethane is developed. Tough, chemically-inert films were prepared from this material. Resonance-enhanced second-harmonic generation coefficients (d 33 ) of approximately 120 pm/V at a 1.064-μm fundamental wavelength were obtained. Using a Mach-Zehnder interferometer, an electrooptic coefficient of r 13 =13 pm/V was measured at a 633-nm wavelength with a 3-kHz modulation frequency, which is in good agreement with that derived from the SHG d 31 (d 31 =d 33 /3) coefficient employing a two-level model. Second-harmonic generation revealed a long-term stability of dipole orientation in an electrically poled and cured film